Photoelectric tube



July 27, 1937. P. L. SPENCER PHOTOELECTRIC TUBE Filed May 51, 1950 Per L. Jive I 61, INVENTOR. W

A TTORNE Y.

Patented July 27, 1937 UNITED STATES PATENT OFFICE Raytheon Production Corporation, Mass., a corporation of Delaware Newton,

Application May 31, 1930, Serial No. 457,937

16 Claims.

This invention relates to a photoelectric tube and to the manufacture thereof. An object of this invention is to devise a tube which will be sensitive to rays rich in the red and infra-red portions of the spectrum, and which will have a large output. Another object of the invention is to devise a method of manufacture of a phototube having these properties.

The sources of light employed in installatio embracing photo-tubes produce radiations rich in rays in the red portions of their spectra. The photo-tubes of the prior art have been found to be only very slightly aifected by the emanations of red rays, and hence the output of such tubes is so decreased that in order to operate them at maximum eificiency it is necessary to carefully select a light source poor in red emanations and rich in blue, violet and u1tra-violet rays. The advantages of a tube which will operate with high efficiency from any convenient source of light are obvious. It has been, found that, if the cathode of such a tube is provided with a layer of pure silver oxide and a suflicient amount of an active alkali metal, such as caesium, adsorbed upon and within the silver oxide layer, the resulting tube will be highly sensitive to all emanations' within the limits of the solar spectrum, including the infra-red.

The invention will be more clearly understood from a study of the single figure of the drawing which shows the construction of a tube made in accordance with the present invention.

In the drawing, l0 represents the envelope of a photoelectric tube constructed in accordance with the present invention, the envelope l0 containing an inert atmosphere under attenuated pressure, and having a re-entrant stem i i, which serves as the press for securing the elements of the tube in position. The atmosphere within the envelope may be either a high vacuum or a monatomic gas, such as argon, helium or neon, or preferably, a mixture of argon and helium containing about helium. If such a. gaseous atmosphere is desired, the pressure thereof is at about mm. of mercury.

Lead-in wires I2, 13 and II are secured to the leads l2a, [3a, and Ma, respectively, which are sealed into the press H, these leads serving the purpose as conductors and supports for the oathode i5, which is preferably formed as a plate, and which is composed of nickel, or other suitable metal. The cathode IB is preferably curved symmetrically with the envelope, and advanta geously takes the form of a half of an open in the press ll.

ended cylinder. This cathode carries the light sensitive materials above referred to.

Lead-in wire I6 is secured to a wire 16a sealed Wire lBa forms the anode of the tube, and is conveniently formed of nickel. In addition to serving as the anode, wire Ilia supports the disc H, which serves both as a shield to protect the cathode from static and magnetic fields, and also serves as a supporting member for the chemicals that provide alkali metal for sensitizing the light sensitive surface of the plate Hi.

The container is represented by a cupped disc l8 secured upon the surface of the disc l1, and is shown as having formed within it, the cup l9 which contains the reagents for providing the sensitizing metal.

The exhaust tube for the envelope I0 is shown at 20, the exhaust tube communicating with the interior of the envelope through the side of the press H, as clearly shown.

The tube is constructed in the following manner: Silver oxide is mixed with nitro-cellulose and amyl acetate to a consistency suitable for applying with an air brush. The mixture is sprayed upon the plate l5, fully covering the surface on the side to be exposed and allowed to dry. After sealing the assembled stem in the envelope, the resulting tube is exhausted and baked at a temperature that will reduce the silver oxide to finely divided particles of pure silver. A temperature range of about 250 C.-300 C. is found to be suitable for this purpose.

The reduction is complete when the brown of the silver oxide has changed to light gray of the reduced silver, which is in a very pure form. A low pressure (approximately 60-75 microns) of pure oxygen is then admitted to the tube and direct current voltage applied with the plate l5 as the negative terminal. Sufficient voltage, e. g. from approximately 500-1000 volts, is applied to ionize the oxygen, and the application of this voltage is continued until the silver particles are again oxidized, and the surface of the plate has become a uniform brown again. The oxygen is again exhausted and the tube again baked at a sufficiently low temperature, e. g. approximately 100 C., to prevent any reduction of the silver oxide when the exhausting is completed.

Before assembling the tube, a reactant mixture of caesium bichromate with a somewhat greater amount of elemental silicon than is required for the reduction of the caesium compound is placed in the depression l9 upon the disc ll. The tube is then assembled and when the exhaustion of the tube is completed after the reduced silver had been oxidized, but before the exhaust tube 20 is sealed off, the reactant mixture of caesium bichromate and silicon is heated to its reactant temperature, about 1000 C. until the caesium has been released. The tube is then heated until the silver oxide has adsorbed the correct amount of caesium, which is determined by the surface of the silver oxide becoming buff in color, and the excess caesium has been exhausted fromthe tube. If a gas tube is desired the proper pressure of a monotomic gas is admitted, and the exhaust tube 20 is sealed off. If a vacuum tube is desired, the gas filling is omitted.

-As herein used, the term red rays is intended to include the infra-red portion of the spectrum as well as the visible red. Also a reactant mixture of caesium chloride and metallic calcium may be employed as the reactant mixture for the release of the caesium, in which case a temperature of about 700 C. will be sufiicient to isolate the caesium.

It will be evident that the construction of the tube can be varied to suit requirements as to shape, etc., and that the materials entering into the construction of the tube can be altered in ways readily suggesting themselves to those skilled in this art, as has been above suggested. The specific description of the invention given herein is merely illustrative of one of its preferred embodiments, and it will be understood that it is intended and desired to embrace within its scope, such modifications and changes as may be necessary to adapt it to varying conditions and uses.

What is claimed is:

1. A photoelectric tube comprising an envelope containing an attenuated atmosphere, a

light sensitive electrode comprising a curved plate provided with a coating of light sensitive material, another electrode spaced from the concave side of the said plate and symmetrically disposed therewith, and a shield disposed over the end of said curved sheet, the said shield carrying reactant materials employed in the coating of the said light sensitive electrode.

2. A photoelectric tube comprising an envelope containing a light-sensitive electrode including a curved plate provided with a coating of lightsensitive material, another electrode spaced from the concave side of the said plate and symmetrically disposed therewith, and a shield disposed over an end of said curved plate.

3. A photoelectric tube comprising an envelope containing a light-sensitive electrode, including a. curved plate provided with a coating of lightsensitive material, another electrode spaced from the concave side of said plate and symmetrically disposed therewith, and a conductive plate disposed at the end of said curved plate, the said conductive plate carrying reactive materials employed in the coating of said light-sensitive electrode. I

4. The process of producing a photoelectric cathode which comprises coating a supporting member with a layer of silver oxide, reducing the oxide to its metal, oxidizing the reduced metal to form a coating of pure silver oxide, and coating this silver oxide with a material sensitive to red rays. I

5. The process of producing a photoelectric cathode which comprises coating a supporting member with a layer of silver oxide, reducing the oxide to its metal, oxidizing the reduced metal to forma coating of pure silver oxide, and coating this silver oxide with an alkali metal,

6. The process of producing a photoelectric cathode which comprises coating a supporting member with a layer of silver oxide, reducing the oxide to its metal, oxidizing the reduced metal to form a coating of pure silver oxide, and coating this silver oxide with caesium.

7. In the production of a photoelectric cathode,

the steps which comprise coating an electrode with silver oxide, inserting the coated electrode into an envelope, reducing the said oxide to metal under a vacuum maintained in the said envelope, oxidizing the reduced metal, and introducing into contact with the resulting oxide, an atmosphere comprising a light sensitive alkali metal.

8. In the production of a photoelectric cathode the steps which comprise forming an electrode assembly comprising a plate electrode, a wire electrode and a disk carried by the said wire electrode, coating the said plate electrode with silver oxide in a uniform layer, inserting the said assembly into an envelope, exhausting the said envelope until the silver oxide is reduced to metal, reoxidizing the said metal with ionized oxygen and bringing the resulting oxide into contact with metallic caesium vapors.

9. A process of producing a light sensitive cathode which comprises uniformly coating a metal sheet with silver oxide, preparing a reactant mixture of a reducible alkali metal and a reducing agent therefor, introducing the coated sheet and reactant mixture into an envelope, exhausting the said envelope while heating above the reducing temperature of silver oxide until the oxide is completely reduced to silver, admitting a low pressure of oxygen into the envelope, ionizing the said oxygen to oxidize the metal, exhausting the excess oxygen while gently heating the envelope and contents, and producing a reaction between the components of the reactant mixture to release the alkali metal contained therein to coat the oxide surface on the sheet.

10. The process of forming a light-sensitive cathode which consists in coating a supporting member with a. layer of metallic oxide, reducing said oxide to its metal, oxidizing the reduced metal, and coating said oxidized metal layer with a light-sensitive material.

11. The process of forming a light-sensitive cathode which consists in coating a supporting member with a layer of metallic oxide, reducing said oxide to its metal, oxidizing the reduced meta1, and coating said oxidized metal layer with an alkali metal.

12. The process of forming a light-sensitive cathode which consists in coating a supporting member with a mixture of silver oxide, nitrocellulose, and amyl acetate, reducing said silver oxide to pure silver, oxidizing said pure silver, and coating said oxidized silver with a lightsensitive metal.

13. The process of forming a light-sensitive cathode which includes depositing upon a supporting surface within a tube a coating consisting of finely-divided particles of pure metal, oxidizing said metal, and coating said oxidized metal with a light-sensitive material.

14. A method of producing a light sensitive electron emissive surface which consists of applying a silver oxide coating to a metallic plate, heating said plate to reduce the silver oxide, placing an atmosphere containing oxygen around the plate and reoxidizing the plate, and subsequently forming a light sensitive surface on the plate.

15. A method of producing a cathode for a light sensitive tube which consists of providing a :ilver oxide coating on the cathode, reducing said lilver oxide, reoxidizing the remaining silver :oating, depositing a film of alkali metal on said 'eoxidized coating, and removing the excess of ;aid alkali metal therefrom.

16. A photoelectric tube which comprises the :ombination with an envelope containing an at- ;enuated atmosphere, of an electrode therein comprising a plate provided with a light-sensitive material upon its surface, an anode symmetrically disposed With respect to said electrode, and a shield carried by said anode and disposed over the end of said plate for shielding said lightsensitive material.

PERCY L. SPENCER. 

